1. Field of the Invention
There is a need for a sheet member which can contain pressure, operate at cryogenic and elevated temperatures, and provide flexibility for repetitive cycles of parallel offset shear translations. Metallic webbings exist which are basically comprised of a plurality of segments or strips interlaced together. However, this type of structure is very porous and cannot contain pressure or liquid. Hence a solid sheet member is needed which has the same type of flexibility as the aforementioned webbed structure.
2. Description of the Prior Art
There are patents which teach how to deal with thermal and physical expansion of containers, panels, and the like. For example, U.S. Pat. No. 3,224,621 describes a cylindrical vessel for the containment of liquid having a temperature differing from ambient temperature. Embossed modular panels accommodate for thermal expansion and have vertical and longitudinal lines or indentations embossed in the material, the intersecting embossed lines being interrupted by circular embossed lines which intersect all four quadrants of the embossed material. The intersection of the embossed lines consists of a ring with radial spokes in the modular panel to relieve forces introduced by thermal expansion or contraction. The embossed pattern all lies in the same plane and therefore does not interrupt all lines of force introduced by shear translation. The panels have limited flexibility for thermal expansion or contraction but do not exhibit or include shear flexibility as does the present invention.
U.S. Pat. No. 3,335,902 relates to beading of cans and the like. Parallel beads or convolutions are superimposed in the axial and circumferential directions of a cylindrical body wall. The beading depth at each intersection of the axial and circumferential convolutions is equal to the algebraic sum of the individual depths. The objective of the convolutions is to add both axial strength and a paneling or buckling resistance. This pattern is fabricated with one convolution superimposed on the other to achieve rigidity in both directions. The beaded structure is different from the shear flexibility material of the instant invention in that there is no radii at the edge of the convolutions, thus resulting in a relatively stiff structure. Structural stiffness is an objective of this prior art patent, while flexibility in shear is a primary objective of the present invention.
U.S. Pat. No. 3,357,593 discloses a means to fabricate a cylindrical structure having tubular wall patterns with helical corrugations which are crosshatched on a tubular wall to resist compressionable and longitudinal forces. Rigidity is introduced with the corrugations and would not provide shear flexibility without spherical reliefs at the convolution intersections. This invention is different than the shear flexibility pattern of the present invention in that the crosshatched corrugations are there to provide rigidity, not flexibility.